Starship Dimensions
http://www.merzo.net/index.html
This site has pictures of all sorts of starships drawn to scale, so you can easily see the size comparisons. There are ships from Star Trek, Star Wars, Babylon 5, and many others, as well as some real-live vehicles and buildings as reference. The ships can be dragged around on the screen. There are screens with scales 10 pixels per meter, 1 pixel per meter, 2 meters per pixel, 10 meters per pixel, 100 meters per pixel, and 2000 meters per pixel.